inabox/InABox.Core/CoreExpression.cs

using Expressive;
using Expressive.Expressions;
using Expressive.Functions;
using InABox.Clients;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace InABox.Core
{
    using FncType = Func<IExpression[], IDictionary<string, object>, object?>;

    public interface IExpressionModel { }
    public interface IExpressionModel<TReturn> : IExpressionModel { }

    public class CoreExpression
    {
        private Expression Expression;

        public IReadOnlyCollection<string> ReferencedVariables => Expression.ReferencedVariables;

        protected virtual Type? ReturnType { get; }

        public CoreExpression(string expressionString)
        {
            Expression = new Expression(expressionString);
            foreach (var (name, function) in _functions)
            {
                Expression.RegisterFunction(name, function);
            }
        }

        public object? Evaluate(Dictionary<string, object?>? variables)
        {
            var result = Expression.Evaluate(variables);
            if(ReturnType != null)
            {
                return CoreUtils.ChangeType(result, ReturnType);
            }
            return result;
        }

        #region Static

        private static List<Tuple<string, FncType>> _functions = new List<Tuple<string, FncType>>();

        static CoreExpression()
        {
            RegisterFunction("Format", (p, v) =>
            {
                if (!(p[0].Evaluate(v) is string format)) throw new Exception("No format string given for Format()");
                return string.Format(format, p.Skip(1).Select(x => x.Evaluate(v)).ToArray());
            });

            RegisterFunction("Client_LoadDocument", Fnc_LoadDocument);
        }

        private static object? Fnc_LoadDocument(IExpression[] p, IDictionary<string, object> v)
        {
            var id = p[0].Evaluate(v);
            if (id is null)
                return null;
            if (!(id is Guid docID))
                return null;

            return new Client<Document>()
                .Query(
                    new Filter<Document>(x => x.ID).IsEqualTo(docID),
                    new Columns<Document>(x => x.Data))
                .Rows.FirstOrDefault()
                ?.Get<Document, byte[]>(x => x.Data);
        }

        public static void RegisterFunction(string name, FncType function) =>
            _functions.Add(new Tuple<string, FncType>(name, function));

        #endregion
    }

    public class CoreExpression<TModel, TReturn> : CoreExpression
        where TModel : IExpressionModel<TReturn>
    {
        protected override Type? ReturnType => typeof(TReturn);

        public CoreExpression(string expressionString): base(expressionString) { }

        public new TReturn Evaluate(Dictionary<string, object?>? variables)
        {
            var result = base.Evaluate(variables);
            if(result is TReturn ret)
            {
                return ret;
            }
            return default(TReturn);
        }
    }
}